Compression Tricks Of The Pros - Part 4

If you’ve ever felt that you’re not getting the best out of your compressor, limiter, gate or de-esser, then this series on compressors is for you. In Part 4, we’ll look at the best way to set up and use gates and de-essers.

Also available in this series:

De-essers

Sometimes a vocal has a short burst of high-frequency energy where the “S’s” are over-emphasized, and this is known as “sibilance.” It comes from a combination of lack of mic technique by the vocalist, poor mic placement, the type of mic used, and heavy compression on the vocal track. Sibilance is nasty sounding and something that’s highly undesirable, so a special type of compressor called a a de-esser is used to combat it (see Figure 1). A properly tuned de-esser works on only a selected narrow band of frequencies between 3k and about 8kHz to eliminate sibilance.

Figure 1: A Typical De-esser

Most de-essers have only two controls; Threshold and Frequency. Threshold sets the level where the de-esser begins to work, while Frequency allows you to select the exact frequency where the sibilance is occurring. Some de-essers also have a button called Listen that allows you to solo only the frequency that’s being compressed, which can be helpful in finding the exact offending frequency range, while others have a Range control, that allows you to set the exact amount of attenuation.

To use a de-esser, here’s what you do:

Solo the lead vocal and insert the de-esser on the channel.

Raise the Threshold control on the de-esser until the sibilance is decreased, but you can still hear the “S’s”. If you can’t hear them, then you’ve raised the Threshold too far.

Scan the available frequencies with the Frequency control until you find the one that’s most offensive.

Un-solo the vocal and listen in context with the track.

At this point one of three things will happen:

The vocal will sound perfectly natural and the sibilance will be gone, but the correct balance of the S’s will remain. If that’s the case, you’ve done a great job and it’s time to move on.

There will still be some remaining sibilance. This means that you’ll have to go through steps 2 and 3 again. Sometimes just an additional small adjustment of either the Threshold or Frequency control is all that’s needed to get the sibilance under control.

You can’t hear any “S’s”. This means that you’ve increased the Threshold control too far and you’ve eliminated all the S’s. You still need a certain amount of them to make the lyrics sound natural and distinguishable. Back off on the Threshold control a bit and you’ll be there.

Gates

Although not used nearly as much in the studio now that digital workstations and console automation are so prevalent, gates are still used a lot in sound reinforcement. A gate is sort of a reverse-compressor in that it keeps a signal turned off until it reaches a predetermined threshold level, then the gate opens and lets the sound through. The gate can be set to turn the sound completely off when it drops below threshold, or set so it just lowers the level a predetermined amount. Depending on the situation, usually turning the level down a bit sounds more natural than turning it off completely, although turning it completely off can be used as a great effect.

A gate (sometimes called “Noise Gate” or “Expander”) is usually used to try to eliminate problems on a track or a mic channel like noise, buzz, coughs or other low level noises off-mic. On loud guitar tracks for instance, a gate can be used to effectively eliminate amplifier noise when the guitar player is not playing. On drums, gates can be used to turn off the leakage into the tom mics since that tends to muddy up the other drum tracks. A gate can also be used to tighten up the sound of a floppy kick drum by decreasing the after-ring.

Many expander/gates (especially plugins) also have what’s know as a sidechain, which is just an additional input called a “key” or “trigger” input that allows the gate to open when triggered from another instrument, channel or processor. This can be really useful, and is frequently used to tighten up the kick and bass in electronic music.

Some expander/gates have a setting called “duck” mode. This is actually another use for the sidechain, but this time the gate stays open until it sees a signal on the key/trigger input and lowers the level of the gate. An example of this is what frequently happens in an airport, where you hear music over the sound system that is automatically decreased (or ducked) when an announcement comes on.

Just like compressors, modern hardware gates are very fast, but plugins have the advantage that they can be designed so that the side-chain 'looks' at the signal a millisecond or two before it arrives at the gate's main input allowing the gate to start opening just before the transient arrives. This “look-ahead” feature is only an advantage when dealing with audio that has a very fast attack, so it is usually switchable or variable when it’s provided.

Like the de-esser, a gate can sometimes consist of just a few controls, principally the Threshold, Range, but sometimes Hold or Release controls as well (see Figure 2). Range sets the amount of attenuation that occurs after the threshold is reached and the gate turns on. Sometimes when gating drums, the Range control is set so it attenuates the signal only about 10 or 20 dB. This lets some of the natural ambience remain and prevents the drums from sounding choked. The Hold control keeps the gate open a defined amount of time, and the Release control adjusts the amount of time until the signal dies out, just like on a compressor.

Figure 2: A Typical Noise Gate

There are three instruments that usually benefit greatly from the addition of a gate in the signal path; the electric guitar, the snare, and the toms. In recording and mixing, thanks to the wonders of the DAW, we can usually either edit or automate away the offending noise or leakage, but that can take a lot of time. It’s sometimes a lot easier to just insert a gate in the signal path to get the same result. Of course, when it comes to live sound you can’t do that, so the gate then becomes an integral part of keeping the noise and leakage at bay.

Here’s how to set up a gate for the instruments mentioned above, although the principle is the same on just about any audio source.

Using A Gate On An Electric Guitar

Solo the electric guitar and insert the gate into the channel signal path, then go to a place in the track (if you’re mixing) where there’s amplifier noise just before the guitar plays.

Raise the Threshold control until the noise is decreased, then move to a place in the timeline where the guitar is playing. If the gate is still engaged and you can’t hear the guitar, then you’ve raised the Threshold too far. Back it off until you can hear the guitar again, then go back to the noisy part and see if you can still hear the noise or if it’s attenuated. If you can still hear the noise, then you’ll have to readjust the Threshold so you can hear the guitar but not the noise when it’s not playing. This can take a few adjustments until you get it right.

Sometimes a gate will switch quickly between it’s on and off state depending on how the controls (mostly the Threshold) are set. This is sometimes called “chatter.” If the gate is chattering, try fine tuning the settings of the Threshold and Release controls (if the gate has one). If it still chatters, add a compressor before the gate to keep the signal steady.

Using A Gate On A Snare Drum

Solo the snare and insert the gate into the signal path of the channel.

Raise the Threshold control until you can hear the snare drum hit, but no sound in between hits. Un-solo the track. Does it sound natural? Does it sound cut off?

Adjust the Range control so the snare is attenuated by 10 dB between hits. If there’s still too much leakage for your taste, increase the range control to around 20 dB or whatever level seems natural.

If the gate chatters, try fine tuning the settings of the Threshold and Release controls (if the gate has one). If it still chatters, add a compressor before the gate to keep the signal steady.

This also works very well on under-snare mics to get rid of the kick drum leakage.

Using A Gate On The Toms

Go to a place in the song where there’s a tom fill. Solo the tom and insert the gate into the signal path of the channel.

Raise the Threshold control until you can hear the tom hit, but no sound in between hits. Un-solo the track. Does it sound natural? Does it sound cut off?

Adjust the Range control so the tom is attenuated by 10 dB between hits. If there’s still too much leakage for your taste, increase the range control to around 20 dB or whatever level seems natural.

If the gate chatters, try fine tuning the settings of the Threshold, and the Hold or Release controls (if the gate has them). If it still chatters, add a compressor before the gate to keep the signal steady.

Using de-essers and gates are a great way to fine-tune your mix, but the setting them up does take some time and experimentation. Because musicians play dynamically, the settings that work on one part of a song can work great, but then seem totally out of whack on another. Don’t get frustrated, just continue to try to find that happy medium. And remember that a compressor before your de-esser or gate can be the trick that really makes it work well.

Some of the above material comes from my book Mixing And Mastering With IK Multimedia’s T-RackS, and my upcoming book The Audio Mixer’s Bootcamp. You can read excerpts at bobbyowsinski.com.